Geneva: The world's worst-ever Ebola epidemic has now infected nearly 6,300 people in West Africa and killed nearly half of them, according to World Health Organisation figures released on Thursday.

In its latest update, the UN health agency said a total of 6,263 people had been infected across five west African countries -- 44 per cent of them over the past three weeks -- and that 2,917 had died.

Here are the latest WHO numbers, as of September 21:

In Guinea, where the outbreak began late last year, Ebola had as of September 21 infected 1,022 people, killing 635 of them.

Nearly a third of those cases surfaced in the three weeks leading up to September 21.

The situation in the country appears to have "stabilised", with between 82 and 102 confirmed and probable new cases reported each week for the past five weeks, WHO said.

In Liberia, which has been hit the hardest by the outbreak, 3,280 people had been infected with Ebola -- more than half in the preceding three weeks -- and 1,677 of them had died.

In Sierra Leone, Ebola had meanwhile infected 1,940 people and killed 593 of them. The three weeks since September 1 accounted for 38 percent of total infections.

The situation in the country "continues to deteriorate," WHO said, blaming especially a sharp increase in the number of new cases reported in Freetown.

New cases and deaths found during Sierra Leone's controversial three-day lockdown -- around 300 according to local officials -- had not yet been included in the WHO data, the agency said.

Nigeria had, as of September 21, recorded 20 cases, including eight deaths, since Ebola first arrived in the country with a Liberian finance ministry official, who died in Lagos on July 25.

The last case confirmed in the country was on September 5.

Senegal's only confirmed Ebola case -- a Guinean student who crossed the border just before it was closed on August 21 -- has recovered, but the country will not be declared free of the virus until 42 days after the case was recorded.